Pilfer-proof plastic cap

Abstract: Disclosed is an improved pilfer-proof plastic cap comprising a cap body (1), a band member (2), and a plurality of stopper tabs (7) disposed inside of the band member. The inventive cap securely strengthens own pilfer-proof function by way of minimizing transit resistance of the stopper tabs on the way of climbing over a bead member (13) of a bottle mouth while securing the cap thereto and also by way of improving force of the stopper tabs to retain the band member. Structurally, an annular wall (5) upwardly opening itself is integrally formed with a band member inside of the band member. Aperture edge of the annular wall is inwardly bent in the radial direction.

Description: BACKGROUND OF THE INVENTION The present invention relates to a plastic cap incorporating pilfer-proof function. As is disclosed in US-A-4,550,844 for example, any of those conventional plastic-molded pilfer-proof caps has a cap skirt and a band member which are integrated by means of a plurality of frangible bridges. More than 10 of stopper tabs are formed on internal wall surface of the band member by way of projecting themselves in the obliquely downward direction. When screwing the cap skirt on bottle mouth, the stopper tabs come into contact with a bead member outwardly expanding itself in the periphery of the bottle mouth, and then reversely bend themselves in the obliquely upward direction. Then, while maintaining bent condition, the stopper tabs climb over the bead member before eventually being engaged with the bottom surface thereof to prevent the band member from being lifted while opening the bottle. Each of the stopper tabs is thin at the bent end. However, the nearer the projected end, the greater the thickness of each stopper tab. Japanese Patent Publication No. HEI3-11985 (1991) discloses a pilfer-proof cap. This prior art forms a plurality of stopper tabs on internal wall surface of a band member in the state projecting themselves in the obliquely upward direction. Like the above example, the nearer the bent end, each of these stopper tabs has thinner surface wall. This is because of the need to minimize transit resistance while the stopper tabs respectively climb over the bead member. Excessive transit resistance causes bridges to easily be torn off while screwing the cap on the bottle mouth. The applicant for a patent related to the present invention previously proposed a pilfer-proof cap via Japanese Laid-Open Patent Application Publication No. HEI1-182259 (1989), which provides a plurality of stopper tabs projecting themselves from bottom edge of a band member in the obliquely upward direction, where surface wall of each stopper tab is bent in the chevron shape in the sectional view. When introducing those stopper tabs each having surface wall being thin at the refracted end and being thicker in the direction of projected end, transit resistance of these stopper tabs can be minimized when climbing over the bead member. On the other hand, there is problem in terms of retentive force of the band member while opening a bottle cap. Concretely, while the band member is pulled in the upward direction relative to a cap opening operation, refracted ends and projected tips of the stopper tabs respectively bend downward. In consequence, the band member shifts upward by such an amount corresponding to the degree of incurred deformation. In an extreme case, the band member is fully disengaged from the secured position. If the stopper tabs were incapable of sustaining enough engaging force, even though the sealed bottles were opened out of mischief while being displayed, nobody can visually identify this. When the band member shifts upward, seal of the cap leaves the bottle mouth before bridges are torn off, thus resulting in the faulty effect of sealing. If this symptom occurs in a bottle containing carbonated beverage, carbonic acid gas will be lost. Unless bridges are torn off, dissipation of carbonic acid gas cannot be identified. In order to provide stopper tabs with greater engaging force, if thickness of bent ends of the stopper tabs were expanded, it will result in the increased transit resistance while the stopper tabs climb over the bead member on the way of screwing the cap on the bottle mouth. If excessive force were applied in order to screw the cap on the bottle mouth, bridges may be torn off. As is apparent from the above, it is a matter of contradiction to minimize transit resistance while the stopper tabs respectively climb over the bead member on the way of capping a bottle and simultaneously provide the stopper tabs with greater engaging force on the way of opening a bottle. On the other hand, according to the cap having surface walls of stopper tabs being folded in the chevron shape, surface walls of the stopper tabs are provided with greater buckling strength than that of conventional plane-shaped stopper tabs, thus permitting the chevron shaped stopper tabs to more securely retain the band member. However, like the above-cited conventional cap, the previously proposed cap is also provided with a number of independent stopper tabs on the internal surface of the band member. In consequence, these stopper tabs bend themselves inwardly or downwardly while opening a bottle to cause the seal to be released before the bridges are torn off. In other words, there was a certain limit in improving strength of the stopper tabs to resist deformation on the way of opening a bottle. EP-A-0390412 discloses a tamper resistant closure according to the first part of claim 1 having an upper cap body, a lower band member, a plurality of bridges, an annular wall and a plurality of stopper tabs; wherein said upper cap body and said lower band member are integrally molded together by said plurality of bridges interposed between said cap body and said lower band member; and wherein said annular wall extends upwardly and inwardly from said lower band member and is integrally formed with said lower band member. However, the stopper tabs project radially outwardly from said annular wall. According to the present invention, said plurality of stopper tabs project inwardly from said annular wall and are formed by inwardly folding the aperture edge of said annular wall in the radial direction, so that each of the stopper tabs consists of a pair of triangular surface walls defined by a ridge line between the pair of walls and border lines between each said surface wall and the annular wall, said ridge line and border lines converging at a base where the annular wall is connected to the band member. The invention provides minimal transit resistance when the stopper tabs climb over a bead member on closing a bottle and ensures the band member is securely retained when opening the bottle. Further, force acting upon the band member when opening the bottle is shared by the annular wall and the stopper tabs. Since the invention increased the load sharing sectional area and provides a bending structure that can hardly be subject to buckling deformation, the band member is more securely retained. When securing the cap to a bottle mouth, the stopper tabs must slide obliquely sideways and downward over the bead member of the bottle. Then, only the folded tips or ridges of the stopper tabs come into contact with the bead member and receive a radially outward reaction force, so that contact resistance is minimised. Furthermore, the stopper tabs can easily be deformed to smooth out the bent shape because the reaction force is concentrated onto the folded ridges thereof, thus minimising transit resistance while securing the cap onto a bottle mouth. The stopper tabs may be respectively formed along the aperture edge of said annular wall in the manner of chevrons. Alternatively, the stopper tabs may be respectively formed in sawtoothed shape with one of said triangular surface walls, which is leading in the cap-closing direction of rotation when screwing said cap to a bottle mouth being mildly inclined, and the other said triangular surface wall comprising a short-length surface wall extending substantially in the radial direction. With these sawtoothed stopper tabs, the mildly inclined surface walls are engaged by the bead member when capping a bottle, and then the surface wall elastically deforms to expand in the radially outward and circumferential directions before smoothly climbing over the bead member. After completing a bottle capping process, the wall surface returns to the original shape while being engaged under the bead member. The magnitude of transit resistance generated in the course of capping a bottle with the cap incorporating the sawtoothed stopper tabs is slightly higher than typically generated by chevron type stopper tabs. On the other hand, stopper resistance of the sawtoothed stopper tabs when opening the cap is greater than that of the chevron-type stopper tabs, thus advantageously improving the pilfer-proof function. Furthermore, transit resistance of the cap incorporating the sawtoothed stopper tabs can be lowered to such a degree substantially corresponding to that of the cap incorporating chevron-type stopper tabs by forming grooves at the intersections of the surface walls of the tabs. The stopper tabs may be provided continuously on said annular wall, or the wall may have circular arc domains between said stopper tabs. Preferably, the cap has a plurality of frangible bridges each being relatively easily breakable and a bridge which is relatively durable. A breakable domain is formed in the band member adjoining a location at which the durable bridge is provided. It is so arranged that the breakable domain and the frangible bridges respectively have break strength less than that of the durable bridge. Since the cap may incorporate the band member accommodating a breakable domain adjacent to a location at which the durable bridge is formed, the break strength of the durable bridge is greater than that of the breakable domain and the bridges, when opening the cap from a sealed bottle, the bridges and the breakable domain are respectively torn off except for the durable bridge that remains unaffected. After the breakable domain is torn off, the band member is disengaged from the bead member. As a result, the band member is eliminated from the bottle mouth via the durable bridge in the state being integrated with the cap body. According to the cap embodied by the invention, since there is less transit resistance on the way of climbing over the bead member, actual break strength of the bridges can be arranged to be lower than that of conventional caps, thus saving force needed to open up the sealed cap. Furthermore, since the band member can securely be prevented from shifting upward by way of solidly securing the band member with stopper tabs and annular walls, it is possible for the inventive cap to expedite the moment to break off bridges. This will effectively help prevent faulty bottled products from easily being generated otherwise cause by incidental mischief for example. In consequence, the invention can provide useful caps capable of securely exerting pilfer-proof function as a whole. Since the band member can also be torn off simultaneous with break of small bridges on the way of opening a sealed bottle, the band member can integrally be removed from the bottle together with the cap body. Examples of the invention will now be described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partially exposed front view of an embodiment of the cap; Fig. 2 is an enlarged sectional view across line A-A shown in Fig. 1; Fig. 3 is an enlarged sectional view across line B-B shown in Fig. 2; Fig. 4 is a pair of enlarged sectional views of the cap representing sequential processes for mounting the cap; Fig. 5 is a partially exposed front view of the cap representing the opened state thereof; Fig. 6 is a front view of the breakable domain of the cap representing the broken state thereof; Fig. 7 is a sectional view of the cap according to a second embodiment of the invention; Fig. 8 is a sectional view of the cap along line C-C shown in Fig. 7; Fig. 9 is a transverse plan representing the stopper tabs according to a third embodiment of the invention; and Fig. 10 is a transverse plan representing the stopper tabs according to a fourth embodiment of the invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figures 1 through 6 respectively illustrate structure of the inventive cap according to the first embodiment. The inventive cap shown in Fig. 1 comprises an upper cap body 1 and a lower band member 2 disposed in opposition from the cap body 1 via minimal clearance, where the cap body 1 and the band member 2 are integrally linked with each other by means of 8 units of bridges 3 and 3a via a plastic molding process. Screw threads 4 are formed on internal surface of the cap body 1. Those bridges 3 and 3a are circumferentially disposed at equal intervals. Of these, 7 units respectively consist of a fine bridge 3 each having narrow width and breakalble strength, whereas the remaining one consists of a bridge 3a having durable strength and width wider than that of the fine bridges 3. The band member 2 is of ring shape, which is integrally formed together with an annular wall 5 continuously being linked with the bottom of inner surface of the band member 2 by way of upwardly opening itself. The annular wall 5 is continuous to the band member 2 via a base 6 folded in V-shape. The whole of surface wall of the annular wall 5 obliquely projects itself in the state upwardly being tapered off. As shown in Fig. 1 for example, thickness of the annular wall 5 according to the first embodiment is arranged to be constant including that of the base 6. However, thickness of the annular wall 5 may be arranged to differ from that of base 6. A plurality of stopper tabs 7 are formed in the annular wall 5 in order to securely retain the band member 2 at bottle mouth. More particularly, by inwardly bending aperture edge of the annular wall 5 in the radial direction to form continuous chevrons. Each of these stopper tabs consists of a pair of triangular surface walls 7a and 7a, where ridge line of a pair of surface walls 7a and 7a and border line between the annular wall 5 and both surface walls 7a and 7a converge themselves at the base 6 in order that the tip of the ridge line can inwardly project itself in the radial direction above other levels. As shown in Fig. 2, it is arranged that thickness T1 of the ridge line is slightly thinner than thickness T2 of the surface wall 7a. The reason is described later on. After securing the cap on bottle mouth, when the cap body 1 is turned to open up the bottle, the bridge 3 is torn off to cause the band member 2 to remain in the periphery of bottle mouth. In the case of this kind of cap, by manually putting the cap body 1 back to the bottle mouth and jointing the torn-off bridge 3 to the cap body 1, the bridge 3 can be shammed as though normally being linked with the cap body 1. In order to prevent intentional abuse of the cap from occurrence, it is desired that the band member 2 can be torn off simultaneous with screwing off the cap body 1 so that the band member 2 can be eliminated from bottle mouth. More particularly, as shown in Figures 2 and 3, the annular wall 5 is split by means of a groove 8 at the band member 2 being adjacent to a point at which the bridge 3a having durable break strength is formed. In addition, a recessed domain 9 continuous to the groove 8 is formed in the band member 2 before forming an easily breakable break domain 10 between them. According to the first embodiment shown in the related drawings, break strength of the breakable domain 10 is arranged to be more than that of those bridges 3 having breakable break strength and conversely to be less than that of the bridge 3a having durable break strength. However, break strength of the breakable domain 10 may also be arranged to be less than that of those bridges 3 each having breakable break strength. The cap is secured on bottle mouth via the sequential steps shown in Fig. 4. The reference numeral 12 shown in Fig. 4 designates screw threads formed on bottle mouth. The reference numerals 13 and 14 shown in Fig. 4 respectively designate a bead member and a packing. After putting the cap on bottle mouth followed by screwed on cap body 1, a plurality of stopper tabs 7 on the internal surface of the band member 2 respectively come into contact with the bead member 13, and as a result, while receiving pressing reaction force from the bead member 13, all the stopper tabs 7 circumferentially shift themselves in the obliquely prone manner. In the course of making circumferentiai shift, since the stopper tabs 7 continuously bend themselves chevron wise, they can easily be subject to elastic deformation in the outward radial direction like bellows for example, and yet, since thickness T1 of the ridge line is thinner than thickness T2 of the surface wall 7a, the stopper tabs 7 can easily be deformed even when receiving slightest amount of pressing reaction force. Furthermore, only the ridge line at the tip of bent stopper tabs 7 comes into contact with the bead member 13. Minimal contact resistance and concentration of pressing reaction force onto the tip of bent stopper tabs 7 to facilitate elastic deformation of the stopper tabs 7 are quite effective to minimize transit resistance of the stopper tabs 7 when climbing over the bead member 13. Accordingly, the bridges 3 can securely be prevented from being torn off otherwise caused by function of excessive tensile force incurred on the way of securing the cap onto bottle mouth. After climbing over the bead member 13, the stopper tabs 7 return to the upwardly inclined posture availing of own elasticity to cause the tips of the bent upper edges to securely be engaged with the base on the bottom surface of the bead member 13. Simultaneously, while being pressed against ceiling wall of the cap body 1, the packing 14 elastically deforms itself to closely adhere to peripheral wall of the bottle mouth. When the cap body 1 is turned to open up bottle, tensil force along circumferential direction acts upon the bridges 3 and 3a. On the other hand, lifting force acts upon the band member 2. The lifting force also acts upon the stopper tabs 7 as buckling load. However, all the stopper tabs 7 bend themselves by way of chevron shape in the section, thus forming reinforced structure that can hardly be subject to buckling deformation. Furthermore, since the stopper tabs 7 are integrated with the annular wall 5, buckling load is cooperatively shared by the stopper tabs 7 and the annular wall 5. Furthermore, deformation strength of the base 6 is reinforced by arranging thickness of the base 6 to be substantially equal to that of the surface wall 7a. In consequence, even when turning the cap body 1 to open up bottle, the band member 2 can securely be held in position without causing itself to shift upward, thus facilitating an early break of the bridges 3. (See Fig. 5) Even after all the bridges 3 are torn off, the other bridge 3a having durable break strength still remains unaffected. In consequence, opening force acting upon the cap body 1 concentrates onto the bridge 3a. The breakable domain 10 on the part of the band member 2 adjoins the bridge 3a. Since break strength of the breakable domain 10 is weaker than that of the bridge 3a, break line generated in local domain adjacent to the bridge 3a grows itself in the direction of the breakable domain 10. Finally, as shown in Fig. 6, the break line cuts the band member 2 at the breakable domain 10. The groove 8 described earlier helps facilitate disconnection of the band member 2. After being split, the whole of the band member 2 becomes loose to cause the stopper tabs 7 to be disengaged from the bead member 13, and thus, the split band member 2 is removed from bottle mouth as of the condition being integrated with the cap body 1 by the bridge 3a. Therefore, even though anyone attempts to recap bottle mouth with the removed cap body 1, since the band member 2 is broken off hang downwardly from the cap body 1, viewers can evidently identify that the cap was already opened up. Figures 7 and 8 respectively designate the second embodiment of the inventive pilfer-proof cap by way of varying the state of disposing the stopper tabs 7. To implement the second embodiment, circular-arc portion 5a and each stopper tab 7 are alternately formed as of the state in which aperture edge of the annular wall 5 can remain in the form of circular-arc, thus decreasing the number of the disposed stopper tabs 7 as the difference from the first embodiment. Except for this difference, all the structures of the second embodiment are exactly identical to those of the cap according to the first embodiment. Figures 9 and 10 respectively designate further embodiments of the inventive pilfer-proof cap by way of varying plan-view configuration of the stopper tabs 7. To implement the third embodiment shown in Fig. 9, in the same way as was done for the second embodiment, stopper tabs 7 are intermittently formed, and then, thickness of the stopper tabs 7 is reduced by forming a groove 7b at a local domain adjacent to a pair of surface walls 7a and 7a, thus facilitating the stopper tabs 7 to easily deform themselves outward in the radial direction. As a matter of course, such a groove 7b may also be provided for the stopper tabs 7 of the first embodiment. To implement the fourth embodiment shown in Fig. 10, a surface wall 7c mildly inclining itself at the upstream side of the cap closing rotating direction on the way of screwing the cap on bottle mouth and a short surface wall 7d extending externally itself substantially in the radial direction are respectively formed before eventually completing sawtoothed stopper tabs 7. As was done for the second embodiment, the fourth embodiment shown in Fig. 10 has formed circular-arc domains 5a between the stopper tabs 7. However, as was done for the first embodiment, the stopper tabs 7 may also be provided in succession. As was described earlier in relation to the first embodiment, not only thinning the breakable domain 10 by provision of a recessed domain 9 or a groove 8 is possible. The breakable domain 10 may also be formed by providing the band member 2 with machine-sewed frail portion. The annular wall 5 may also be of such a structure as the one upwardly projecting itself on the halfway of the vertical-directional inner wall surface of the band member 2.

Claims: A pilfer-proof plastic cap comprising; an upper cap body (1); a lower band member (2); a plurality of bridges (3,3a); an annular wall (5); and a plurality of stopper tabs (7); wherein said upper cap body (1) and said lower band member (2) are integrally molded together by said plurality of bridges (3,3a) interposed between said cap body (1) and said lower band member (2); and wherein said annular wall (5) extends upwardly and inwardly from said lower band member (2) and is integrally formed with said lower band member (2); characterised in that said plurality of stopper tabs (7) project inwardly from said annular wall (5) and are formed by inwardly folding the aperture edge of said annular wall (5) in the radial direction, so that each of the stopper tabs (7) consist of a pair of triangular surface walls (7a) defined by a ridge line between the pair of walls (7a) and border lines between each said surface wall (7a) and the annular wall (5), said ridge line and border lines converging at a base (6) where the annular wall (5) is connected to the band member (2). The pilfer-proof cap according to Claim 1, wherein said plurality of stopper tabs (7) are respectively formed along the aperture edge of said annular wall (5) in the manner of chevrons. A pilfer-proof cap according to the Claim 1 wherein said plurality of stopper tabs (7) are respectively formed in sawtoothed shape with one of said triangular surface walls (7c), which is leading in the cap-closing direction of rotation when screwing said cap to a bottle mouth, being mildly inclined, and the other said triangular surface wall (7d) comprising a short-length surface wall extending substantially in the radial direction. A pilfer-proof cap according to either of Claims 2 and 3, wherein the annular wall (5) has circular arc domains (5a) between said stopper tabs (7). A pilfer-proof cap according any of Claims 1 to 3, wherein said plurality of stopper tabs (7) are provided continuously on said annular wall (5). The pilfer-proof cap according to any preceding claim, wherein said cap body (1) is linked with said band member (2) via a plurality of frangible bridges (3) each being relatively easily breakable and a bridge (3a) which is relatively durable; wherein a breakable domain (10) is formed in said band member (2) adjoining the location at which said durable bridge (3a) is provided; and wherein said breakable domain (10) and said plural frangible bridges (3) have break strength less than that of said durable bridge (3a).

Inventors: TAKANO TAKAFUSA, TAKANO, TAKAFUSA
Applicants: YAMAMURA GLASS CO LTD, YAMAMURA GLASS CO. LTD.
Application year: 1994
Main classification: B65D41
IPC codes: B65D41